如何使用path_provider包在flutter中构建登录页面以将登录信息存储在本地文件中

Question

I have created a save method and read method for storing credentials.

In the code below username and password are going to be saved in a file.

Code is also giving the directory path where it is going to be stored but it is not working properly while tapping on the login button. The code represents the login screen which appears when we open the app for the first time. The user account login page will open after filling the credentials. It will never ask to the user for logins till the user clear the data or uninstall the app. In this code username and password are the text filed, their is a checkbox in the login screen which will act as a remember me box. It will call the save method on click and now I want that checkbox will save credentials only after pressing the login button.

  class  LoginPageState extends State<LoginPage> {
  TextEditingController username = new TextEditingController();
  TextEditingController password = new TextEditingController();

  bool checkValue = false;
  String user ="username";
  String pass="password";


 @override
  void initState() {
    super.initState();
    // call credentials method
    readuser().then((String value) {
      setState(() {
        user="username";
        user = value;
      });
    });
    readpass().then((String value) {
      setState(() {
        pass="password";
        pass = value;
      });
    });
  }

  bool checkingdata() {
    if (user.length !=0 && pass.length != 0) {
      return true;
    } else {
      return false;
    }
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        elevation: 0.0,
        backgroundColor: Colors.white12,
      ),
      body: new SingleChildScrollView(
        child: _body(),
        scrollDirection: Axis.vertical,
      ),
    );
  }

  Widget _body() {
    return new Container(
      padding: EdgeInsets.only(right: 20.0, left: 20.0),
      child: new Column(
        mainAxisAlignment: MainAxisAlignment.start,
        children: <Widget>[
          new Container(
            margin: EdgeInsets.all(30.0),
            child: new Image.asset(
              "assets/images/flutter_icon.png",
              height: 100.0,
            ),
          ),
          new TextField(
            onSubmitted: (_) {
              setState(() {
                user = username.text;``
              });
            },
            controller: username,
            decoration: InputDecoration(
                hintText: "username",
                hintStyle: new TextStyle(color: Colors.grey.withOpacity(0.3))),
          ),
          new TextField(
              controller: password,
              obscureText: true,
              onSubmitted: (_) {
                setState(() {
                  pass = password.text;
                });
              },
              decoration: InputDecoration(
                  hintText: "password",
                  hintStyle:
                  new TextStyle(color: Colors.grey.withOpacity(0.3)))),
          new CheckboxListTile(
           value: checkValue,

            title: new Text("Remember me"),
            controlAffinity: ListTileControlAffinity.leading,
            onChanged: (bool value) { checkingdata();

              _saved(user, pass);
            },
          ),
          new Container(
            decoration:
            new BoxDecoration(border: Border.all(color: Colors.black)),
            child: new ListTile(
              title: new Text(
                "Login",
                textAlign: TextAlign.center,
              ),
              onTap: _saved(user, pass),
            ),
          )
        ],
      ),
    );
  }

  //for username
  _saved (String text,String text2) async {
    print("asggd");
    final userfile = await _localFile;
      //print("asd");
    // Write the file.
    _savedpass(text2);
    print("asded");

    return userfile.writeAsString(text);
  }
  //for password
  _savedpass(String text) async {
    final passfile = await _localFile;
    // Write the file.
    return passfile.writeAsString(text);
  }

  Future<String> readuser() async {
    try {
      final userfile = await _localFile;


      // Read the file.
      String contents = await userfile.readAsString();

      return contents;
    } catch (e) {
      // If encountering an error, return 0.
     //return "dfd";
    }
  }

  Future<String> readpass() async {
    try {
      final userpass = await _localFile;


      // Read the file.
      String contents = await userpass.readAsString();

      return contents;
    } catch (e) {
      // If encountering an error, return 0.
      //return;
    }
  }Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();
    return directory.path;
  }
  Future<File> get _localFile async {
  var _localPath;
  final path = await _localPath;
  return File('$path/counter.txt');
}
}

Read function is used for the testing purposes. It will print the login credential on the home screen. I also want to add one more method in this code which is used to check the saved login credentials form the file so that next time when you reuse the app it will directly open the home screen.

Answer 1

Putting aside the fact that you want to store your credentials in plaintext in a local file, your problem is your _localFile getter. You define a local variable _localPath, so in the next line of code, all you're getting is null . Also, you probably want to create your file if it doesn't exist, simply by calling file.create() .

Answer 2

you may not have the file counter.txt , so you need to create it first. I would advise you to use shared_preferences or hive to store your data.

For example with shared_preferences it will looks like in snippet below:

To retrieve data

final prefs = await SharedPreferences.getInstance();

final login = prefs.getString('login');
final password = prefs.getString('password');

// It's important to check it to the null

if (login != null && password != null) {
  // Use it
}

To store new data

final prefs = await SharedPreferences.getInstance();

await prefs.setString('login', login);
await prefs.setString('password', password);

And you can remove from the preference as well:

final prefs = await SharedPreferences.getInstance();

await prefs.remove('login');
await prefs.remove('password');